💬 👋 We’re always here. Join our Discord to connect with other students 24/7, any time, night or day.Join Here!

Get the answer to your homework problem.

Try Numerade free for 7 days

Like

Report

$\bullet$ The siren of a fire engine that is driving northward at30.0 $\mathrm{m} / \mathrm{s}$ emits a sound of frequency 2000 $\mathrm{Hz}$ . A truck in frontof this fire engine is moving northward at 20.0 $\mathrm{m} / \mathrm{s}$ . (a) What isthe frequency of the siren's sound that the fire engine's driver hears reflected from the back of the truck? (b) What wavelength would this driver measure for these reflected sound waves?

a) $f_{\text { engine }}=2120.7 \mathrm{Hz}$b) $\lambda_{\text { behind }}=0.176 \mathrm{m}$

Physics 101 Mechanics

Chapter 12

Mechanical Waves and Sound

Periodic Motion

Mechanical Waves

Sound and Hearing

University of Washington

University of Sheffield

University of Winnipeg

Lectures

04:16

In mathematics, a proof is…

04:48

In mathematics, algebra is…

04:31

The predominant frequency …

02:19

(I) The predominant freque…

01:35

A fire truck is moving at …

01:58

04:35

A police car is traveling …

04:40

A driver travels northboun…

04:00

A fire truck's siren …

04:17

(a) What frequency is rece…

03:31

An ambulance moving at 42 …

06:29

The siren on an ambulance …

06:04

A siren emitting a sound o…

03:57

A car is parked 20.0 m dir…

10:07

A police car sounding a si…

01:46

An ambulance traveling at …

A fire station's sire…

02:14

A car drives at a speed of…

We're told that a siren of a fire engine that is driving northward at 30 meters per second and met the sound frequency at to kilohertz a truck in front of this. Fire engines moving northward in the same direction at 20 meters per second. And a We want to figure out what the frequency of the siren sound that that fire engines driver here's reflected back from the truck reflected from the back of a truck. So we have our fire engine here with its siren blaring our truck here. Now we have sound coming out of here, hitting the back of the truck and then reflecting back. So depending on the listener is and who the what the source is, we're not sure exactly what the signs of these velocities will be. So we look at it in the first case. In the first case, we have the car here, or the truck is the listener because we're trying to figure out what sound hits the back of it. So the truck is a listener, and so then positive is in This R is in this direction. So we have our formula with for the Doppler effect here but you're positive is in this direction. And then the speeds are both gonna be negative and speed of sound. And there's 344 meters per second. So 324 meters per second, divided by 314 meters per second. We don't have to worry about units here because they can't as long as these are all in the same units were okay and times 202,000 hertz. And we get 2000 63.69 Hertz. No, we've got to take a look at what happens now. We know what the frequency you're bouncing off the back of the truck is now. It's coming back here, and truck is the source, and the fire engine driver is the list. So now ex is positive that that way so we can write. Our are the new sound that the fire truck drivers here it's the frequency of the fire truck crime. And we know that that is our Doppler effect, given the frequency bouncing off the back of the truck and because X is now positive this way, these air both positive. And so we get 374 meters per second, divided by 364 meters per second time's the frequency bouncing off the back of the truck. And that gives us 2120 hertz. Now they ask what wavelength with the driver measure for these reflected Well, that's an easy one to do. We know that the wavelength is just the velocity of the up the the sound of air, their frequency of the the blast minus the velocity of the car or the truck cotton divided by the frequency coming off the truck. And so we have that this is a minus. Sign here because of the direction and so that you see is minus 20. So we get 364 meters per second, divided by the frequency that was acting at the truck. Um and so we get a wavelength of 0.176 meters

View More Answers From This Book

Find Another Textbook

Numerade Educator

In mathematics, a proof is a sequence of statements given to explain how a c…

In mathematics, algebra is one of the broad parts of mathematics, together w…

The predominant frequency of a certain fire truck's siren is 1650 Hz wh…

(I) The predominant frequency of a certain fire truck's siren is 1350 H…

A fire truck is moving at $35 \mathrm{m} / \mathrm{s}$, and a car in front o…

(I) The predominant frequency of a certain fire engine'ssiren is 15…

A police car is traveling east at $40.0 \mathrm{m} / \mathrm{s}$ along a str…

A police car is traveling east at 40.0 m/s along a straight road, overtaking…

A driver travels northbound on a highway at a speed of $25.0 \mathrm{m} / \m…

A driver travels northbound on a highway at a speed of 25.0 m/s. A police ca…

A fire truck's siren at rest wails at $1400 \mathrm{Hz} ;$ standing by …

A driver travels northbound on a highway at a speed of 25.0 $\mathrm{m} / \m…

(a) What frequency is received by a person watching an oncoming ambulance mo…

A police car is traveling east at 40.0 $\mathrm{m} / \mathrm{s}$ along a str…

An ambulance moving at 42 m/s sounds its siren whose frequency is 450 Hz. A …

The siren on an ambulance is emitting a sound whose frequency is 2450 Hz. Th…

A siren emitting a sound of frequency 1000 Hz moves away from you toward the…

A car is parked 20.0 m directly south of a railroad crossing. A train is app…

A police car sounding a siren with a frequency of 1580 Hz is traveling at 12…

An ambulance traveling at $44 \mathrm{m} / \mathrm{s}$ approaches a car head…

A fire station's siren is blaring at $85 \mathrm{Hz}$. What's the …

A car drives at a speed of 25 m/s along a road parallel to a railroad track.…

04:45

A firefighting crew uses a water cannon that shoots water at 25.0 $\mathrm{m…

05:10

\cdotse: Leaping the river, II. A physics professor did daredevil stunts in …

04:28

Two point charges $q_{1}=$ $+2.40 \mathrm{nC}$ and $q_{2}=-6.50 \mathrm{nC}$…

00:55

(1) The age of the universe is thought to be about 14 billion years. Assumin…

05:11

$\bullet$ $\bullet$ Ski jump ramp. You are designing a ski jump ramp for…

05:28

Two stationary point charges of $+3.00 \mathrm{nC}$ and $+2.00 \mathrm{nC}$ …

01:24

A 2.20$\mu \mathrm{F}$ capacitor is connected across an ac source whosev…

00:25

$\bullet$ You have a special lightbulb with a very delicate wire filament. T…

07:14

(a) A set of point charges is held in place at the vertices of an equilatera…

02:53

Two very large charged parallel metal plates are 10.0 $\mathrm{cm}$ apart an…